Visual perceptual learning (VPL) by training on a task is interfered with by another training if it occurs within one hour after the initial training. This indicates that VPL is fragile immediately after training but is stabilized within one hour so that it becomes resilient against interference. However, already stabilized VPL of a task becomes susceptible to interference by practicing a small number of the task again (Bang et al, 2013, VSS). Although this so-called reactivation has made us reconsider a role of stabilization/consolidation in VPL, the neural mechanism has yet to be clarified. Here, we examined excitatory and inhibitory processing associated with reactivation. There were psychophysical and brain-imaging experiments. The psychophysical experiment lasted 3 days. On Day 1, subjects were trained on a detection task (2IFC) on orientation A with 16 blocks in staircase. On Day 2, subjects were asked to perform 3 blocks on orientation A for reactivation and then were trained on orientation B. On Day 3, performance on orientations A and B was measured. In the bran imaging experiment, using functional magnetic spectroscopy, we measured the concentration of glutamate and GABA in the early visual cortex before, immediately after and 3.5 hours after the reactivation. An E(excitation)/I(inhibition) ratio in the early visual cortex was taken by dividing the concentration of glutamate by that of GABA. Performance on orientation A significantly decreased between Days 2 and 3, indicating that reactivation makes already stabilized/consolidated VPL of orientation A labile to interference again. The E/I ratio increased immediately after reactivation of VPL of orientation A, and then returned to the baseline level 3.5 hours later. This time course changes are similar to those for stabilization after the first training (Shibata et al, 2015, VSS), suggesting that the neural mechanism of reactivation is similar to that of stabilization.